This invention relates to measurement of physiological data in general, in particular to measurement of data representative of the circulatory system, and specifically to photoelectric measurement of the blood volume waveform of the circulatory system. The circulatory system is contained in a continuous endothelial sac from the heart to the terminal microcirculation ending in the capillaries and venules. The covering of the endothelial sac varies from the thick muscular covering of the heart to no covering at all in the capillaries.
The control of the microcirculation, i.e., small arteries and veins, arterioles and meterarterioles, is essentially muscular and primarily neurogenic. The capillaries respond to local cellular needs, i.e., pH, O.sub.2 levels and nutritional needs. The microcirculation functions to sustain life itself, the larger components of the system are merely subservient to local needs.
The function of blood pressure, i.e., heart action and compliance of larger vessels, are secondary to local needs of perfusion. These needs vary from second to second, from organ to organ; but the end result of all body functions is to maintain homeostasis of the total organism. As the organism ages or changes in response to any condition of stress or environment, drugs, disease, etc., the microcirculation makes compensatory corrections to meet these conditions of cellular demand. The microcirculation makes this change long before central reactions are noted in a compensatory way; indeed the central reactions are ultimately fixed in response to the continuing cellular demand of an aging or disease process. These same demands are evidenced in an acute way, i.e., shock, surgery or sudden environmental changes, usually well in advance of central changes.
By measuring changes in the microcirculation as they occur, it is possible to anticipate and correlate diagnosis and treatment of a great number of body conditions. Many ways have been devised to measure circulatory change; commonly used blood pressure cuffs, indwelling venous and arterial catheters, fiber optic catheters, angiography, dye dilution techniques, glass electrodes on muscle tissue, retinal microscopy, E.C.G., Doppler principle transducers, Wheatstone bridge plethysmography, microsurgery in animals, and many more. With few exceptions, most highly accurate techniques are invasive and are concerned mainly with the "large" circulation and its changes, changes brought about for the most part by demands of the microcirculation in response to life itself.
The present invention provides an apparatus for practicing a non-invasive, rapid technique for measuring microcirculatory homeostasis or change. It operates by the simple topical application of a probe on the skin, and includes circuitry which enables the user to "read" the microcirculation in any suitable area of the body.